Introduction
Planar phased-array antennas are constructed by arranging many, even thousands, of radiating elements spaced in a plane. In operation, the output of each element is controlled electronically. The superposition of the phase-controlled signals from the elements causes a beam pattern that can be steered without any physical movement of the antenna. Line arrays are also possible wherein a single row of antennas and modules make up a steerable array.
Electronically steerable phased array antennas at microwave and higher frequencies have had very limited use due to their high cost and due to difficulties of integrating the required electronics, radiating structures, and RF, DC, and logic distribution networks particularly at frequencies higher than 10 GHz. The spacing required between radiating elements for phased arrays that must steer over wide scan angles is on the order of 1/2 wavelength. The receive electronics or transmit electronics for each radiator must be installed within the projected area corresponding to the interelement spacing. In the case of radar, both receive and transmit electronics must occupy this limited space.
The array of radiating elements are generally protected at their interface with free space by a dielectric cover (radome) and/or a spatial filter, called a frequency selective surface. The electronics (usually in the form of modules containing amplifiers and phase shifters) are electrically connected to and located behind or beside the radiating elements. Networks are located in the same plane or behind the electronics to distribute RF, DC, and steering logic control. The packaging approach must also provide means for venting or controlling the unwanted thermal energy produced within the electronics.